When metal materials, e.g., steel materials, are transferred from, for example, a steel-making step to a subsequent metal manufacturing process, such as a rolling step, which is a subsequent step in an iron-making process, the steel materials are first kept in temporary storage sites called yards and thereafter are carried out from the yards according to the processing time of the subsequent step, for example, according to the processing time of the rolling step where that is the subsequent step. An example of layout of the yards is shown in FIG. 5. As shown in FIG. 5, the yards are storage spaces 501 to 504 demarcated vertically and laterally as buffer areas for supplying the steel materials such as slabs delivered from an upstream step to a downstream step. Vertical segments and lateral segments are often called “columns” and “rows” respectively. Specifically, cranes (1A, 1B, 2A, 2B) are movable in the rows to transfer the steel materials between different columns in the same row. Further, the steel materials are transferred between the rows by transfer tables. When a transfer command is created, “row” and “column” are designated to indicate where to transfer the steel materials (refer to the parenthetical numbers (11), (12), (21), and (22) appended to the storage spaces 501 to 504 in FIG. 5).
Next, a basic work flow in the yards is shown, taking FIG. 5 as an example. First, the steel materials carried out from a continuous casting machine 510 in a steel-making step being a pre-step are carried to the yard by a reception table X via a piler 511, are transferred to any one of the demarcated storage spaces 501 to 504 by the crane 1A, 1B, 2A, 2B to be stacked there. Then, according to a manufacturing schedule of the rolling step being a post-step, they are placed again on a delivery table Z by the crane 1A, 1B, 2A, 2B to be transferred to the rolling step. Generally, the steel materials are placed in the stacked state in the yard as described above. This is intended to make an effective use of a limited yard area. On the other hand, when the steel materials are stacked, in order to facilitate their supply to the subsequent step, it is naturally necessary that their stacking order from the top needs to be the order in which they are processed in the subsequent step. Here, dividing the steel materials into a plurality of piles is called pile sorting.
In the present application, the term “main pile” means final pile where they are stacked for delivery to the subsequent step (also called a delivery pile). In the present application, the term “original pile” means pile that has already been formed in the yard at a present moment. Therefore, the original piles include a main storage part and a temporary storage part. In the present application, the term “temporary pile” means pile for forcible temporary storage at the time of the transfer from the original pile or the reception table to the main pile at and after the present moment.
In the pile sorting process performed in the yard in order to smoothly deliver the required steel materials to a post-step, it can often happen that the originally scheduled steel materials do not arrive because the steel materials scheduled to arrive are downgraded (because of a quality trouble or the like occurring when the steel materials are manufactured, they are downgraded and the originally planned use is changed to another use), the steel materials scheduled to arrive require a precise adjustment process that is not scheduled, and a size change occurs. Further, it cannot be expected almost at all that the state of the storage spaces of the yard changes without any trouble as originally scheduled, and it is an everyday event that unexpected steel materials are forced to be placed on unscheduled storage spaces.
Therefore, as a method to cope with such a situation, frequent re-scheduling (at intervals of several minutes) is performed to readjust a delivery pile appearance (main pile appearance) and a transfer procedure for creating it.
In particular, in order to reschedule the procedure of transfer processes for realizing the delivery pile appearance (main pile appearance), it is necessary to assume many transfer processes required to realize the delivery pile appearance from various states in the yard and to efficiently decide their execution order.
Such rescheduling of the procedure of the transfer processes is a problem difficult to solve in no small way for the following reasons, and a wrong solution could cause congestion of the reception tables, congestion of the transfer works due to the occurrence of a transfer load exceeding the capacity of the cranes, and a failure in the yard management because no storage space is found in the yard.
Reasons why this rescheduling problem is difficult to solve are that, firstly, in the yard, some steel materials are placed in a temporary storage state (a pile state in which they are temporarily stacked until an appropriate timing comes though they are finally separated to be transferred to respective delivery piles), and some others are placed as the main storage (part of the delivery piles), and it is necessary to find to which (temporary storage or main storage) each of the steel materials belongs and decide the transfer order of the steel materials so that the steel materials for the temporary storage come to have a delivery pile appearance most efficiently (with the minimum number of transfer times). Further, since the delivery pile is sometimes formed by the mixture of steel materials already present in the yard and steel materials which are to arrive in the yard later, the aforesaid rescheduling cannot be decided only based on the steel materials which have already arrived at the yard, and has to be decided in consideration of the steel materials which are scheduled to arrive later. That is, the rescheduling has to be performed in consideration of the mixture of both the transfer of the steel materials which have already arrived (relocation process) being a static factor and the transfer of the steel materials which are scheduled to arrive (reception process) being a dynamic factor. Therefore, only with the relocation process (static factor), the re-stacking is done by performing the transfer in a physically handleable order in consideration of the stacked state, but when the steel materials which have not yet arrived and the steel materials which have already arrived are mixed, the arrival timing of the steel materials which have not yet arrived has to be found and the relocation process (decomposition process of the original pile) has to be performed in consideration of the arrival timing, and accordingly the timing of the relocation process cannot be easily decided either.
Variations of the transfer process of the materials to arrive include a case where they can be transferred directly to the main pile (delivery pile) from the reception table and a case where they have to be once transferred to and temporarily stored at a place (temporary pile) different from the main pile at the time of the reception and have to be transferred to the main pile when an appropriate condition is ready. Further, variations of the transfer process of the already arriving materials also include a case where they need not be moved from the original pile, a case where they can be transferred directly to the main pile from the original pile, and a case where they need to be once transferred to and temporarily stored at a place (temporary pile) different from the main pile before transferred to the main pile.
As described above, when the temporary storage is required, the transfer needs to be performed twice, that is, the transfer from the reception table or the original storage place (original pile) to the temporary storage place (temporary pile) and the transfer from the temporary storage place (temporary pile) to the main pile, and in order to reduce the total number of transfer times, it is important to reduce such a case.
Serious situations when a transfer plan of the steel materials in the yard is not appropriate includes a case where it is not possible to reserve the storage space in the yard because the number of steel materials to be temporarily stored is too large or the temporary storage time becomes too long, resulting in a failure in the yard management. Further, there may be a case where the reception tables are congested because the relocation process in the yard takes too long a time and the reception process cannot be handled, causing a situation where a pre-step is forced to be stopped. Giving a great adverse effect to the production, all of these cases are situations that have to be prevented by all means. Therefore, it is important to appropriately make a transfer plan of the steel materials in the yard.
In a conventional practice, a person in charge of planning makes a steel material transfer plan for the pile-sorting of steel materials by trial and error, based on information on steel materials which are to be received in a yard, information on steel materials already placed in the yard, and information on a delivery pile appearance (main pile appearance). However, in such manual planning, it has not been often possible to prepare an “efficient” transfer plan when the number of the steel materials that are targets of the planning is large and the number of transfer times is large. Further, since the preparation of the plan requires skill, an individual difference occurs in the prepared plans, and depending on a preparer of the plan, there occurs a problem that the yard cannot be effectively used and no storage place is reserved. There is another problem that it takes a long period to cultivate a skilled person in charge. Incidentally, the “appropriate” transfer plan here means that the number of transfer times, the temporary storage space, and the temporary storage time are reduced as much as possible without causing the reception congestion, in realizing the delivery pile appearance from the current state of the yard piles.
As a storage space management method requiring these, several methods have been developed. An art described in Japanese Laid-Open Patent Publication No. 06-179525 (“JP 06-179525”) is a basic one in which products are stacked in order so that no stack shifting occurs at the time of the delivery, by using an information file regarding stacking. Japanese Laid-Open Patent Publication No. 2000-226123 (“JP 2000-226123”) also proposes a very basic storage space management method to form articles in a large lot into a single pile to prevent the articles in the large lot from being stacked on an upper side of articles in a small lot, thereby reducing a relocation work at the time of shipping.
Further, Japanese Laid-Open Patent Publication No. 11-255336 (“JP 11-255336”) proposes a steel sheet stacking planning method whose object is to prepare an optimum stacking order plan satisfying conditions at the time of the stacking in a yard, automatically and in a relatively short time even when the number of steel sheets that are targets of the plan becomes enormous. This art adopts a procedure in which the steel sheets are grouped based on conditions such as sizes and the rolling order of the steel sheets, a plurality of arrangement patterns different in the arrangement order of the groups are prepared, simulations in which the stacking is started from the top group of each arrangement pattern are conducted based on stacking determination conditions, and based on the result thereof, the number of piles is found for each of the arrangement patterns, the arrangement pattern with the minimum number of piles is selected, further a predetermined number of the arrangement patterns are selected in ascending order of the number of piles from the prepared arrangement patterns, the group arrangement orders are changed among the selected arrangement patterns to prepare a plurality of new arrangement patterns, and the arrangement pattern with the minimum number of piles is similarly selected from these prepared arrangement patterns and the arrangement pattern with the minimum number of piles.
Further, Japanese Laid-Open Patent Publication No. 2007-84201 (“JP 2007-84201”) proposes a storage space management method including: a pile sorting step of deciding how slabs should be allocated to piles; a lot dividing step of deciding how the slabs should be divided into transfer lots; a lot generation order deciding step of deciding in what order the transfer lots decided by the lot dividing step should be generated; a work instruction generating step of generating a work instruction of a handling apparatus for executing the lot generation order decided in the lot generation order deciding step; and a vacant address deciding step of deciding to which place obstructive slabs should be evacuated while target slabs are taken out.
Further, Japanese Laid-open Patent Publication No. 2008-260630 (“JP 2008-260630”) discloses a method to realize pile sorting in which steel materials that are targets of the pile sorting are regarded as a set, steel material subsets being subsets of this set are first generated, and after feasible piles being subsets satisfying a stacking constraint are subsequently extracted out of the steel material subsets, an optimum solution as the optimum subset of the feasible piles in view of storage space management is calculated.
Finally, Japanese Laid-Open Patent Publication No. 2010-269929 (“JP 2010-269929”) discloses an art in which, in a pile sorting plan, an objective function having both an index for maximizing a pile height and an index for minimizing the number of transfer times realizing this is set, it is made to result in a mathematical programming problem satisfying a constraint condition regarding stacking and transfer, thereby optimizing the pile sorting and the transfer order simultaneously.